Is it permissible for a Muslim female doctor to treat men if she adheres to the Islamic head covering (hijab), is assisted by a female nurse, and limits her treatment to the mouth and teeth without direct touch, except with an intervening barrier? And is her work in a hospital where she cannot choose patients considered a necessity or need that permits this?

We have previously issued a fatwa (definition) stating that it is not permissible for a female dentist to treat a man unless there is a necessity or need. Your work in a hospital where you cannot choose the patient's gender may be an excuse for you as long as you are in need of the work, while striving to convince the administration to assign you to treat women only.